1. Field of the Invention
The present invention relates to an encoding processing apparatus encoding image data, and a decoding processing apparatus decoding the encoded image data.
2. Description of Related Art
In variable-length encoding processing in encoding processing of encoding image data compliant with encoding schemes, such as JPEG (Joint Photographic Experts Group) and MPEG (Moving Picture Experts Group), syntaxes are generated from bitstreams by referring to a variable-length code table. For example, in processing of variable-length-encoding DCT (Discrete Cosine Transform) coefficients for the encoded image data, since the processing is the one for performing on macroblock-level syntaxes, the variable-length code table becomes large in size and thus a search processing time becomes also enormous. Particularly, when such search processing is performed by using a general-purpose computation processor, the search processing cannot be performed parallelly, but performed sequentially from the variable-length code table stored in a cache, thereby increasing a processing cycle count.
In order to reduce the time for searching a variable-length code table in decoding processing, Japanese Unexamined Patent Application Publication No. JP H06-152988 (Patent Document 1) discloses a decoding processing apparatus achieving higher-speed search processing by dividing a coded table by the numbers of “1” or “0” consecutively listed from the top of a target bitstream for variable-length decoding processing.
However, in the decoding processing apparatus disclosed in the Patent Document 1, processing steps in which the numbers of “1” or “0” consecutively listed from the top of the target bitstream are obtained first, then a first table is referred by using the obtained value as an address, a second table is referred by using the information obtained by reference, and further a run length is associated with a level for the string of variable-length code bits, has to be performed with respect a Huffman code table provided in advance.
When such processing steps are performed for a general-purpose processor, processing for a run length/level pair requires a processing time of several tens of cycles. In this way, in the processing compliant with the macroblock-based syntaxes, search processing for run-length and level occupies a relatively large percentage. As such, when encoding processing is performed on high-resolution image data, such a general-purpose processor also performs processing other than the variable-length encoding processing, it would become difficult to perform the encoding processing at real time.
Further, in addition to the variable-length encoding processing, the encoding processing includes a step of calculating encoded information by searching a table associating input/output relation of encoded information calculated at an intermediate processing stage. Thus, in the general-purpose processor, in order to perform encoding processing and decoding processing at real time., a reduction of time required for the search processing is required.